1. Field of the Invention
The invention relates to trial components for joint implants and prosthesis, in particular to trial components for shoulder implants and prosthesis.
2. Description of Relevant Art
The shoulder joint is a ball-and-socket joint, which has an exceptional range of motion. Shoulder instability and other maladies of the shoulder joint, such as arthrosis or fracture, may require a replacement of the joint. Also, other joints other than a shoulder joint may require a replacement.
A shoulder joint prosthesis, which includes the replacement of the convex head of the humerus, is disclosed in U.S. Pat. No. 7,819,923. It reflects the orientation and the center of rotation of actual joints. In the case of a worn or damaged rotator cuff or too much bone loss, such a prosthesis would not recover the range of motion. In such a case, a reverse shoulder prosthesis may be preferable. An example of such a prosthesis is disclosed in the US patent application publication 2009/0210065 A1. In such a prosthesis the humeral component includes a stem and a cup attached to the stem. The glenoid component supports a convex head, which articulates with the cup of the humeral component.
In general, the geometry of the prosthesis has to be adjusted to the patient's needs. This may be done by inserting trial liners into the socket part of the joint. The European patent application EP 2 047 827 A1 discloses an expandable trial component which can be adjusted by rotation. It allows a precise adjustment in size, but the reproducibility is poor, as the height cannot precisely be reconstructed after the trial component has been removed from the joint.
The international patent application publication WO 2007/084939 discloses to provide a plurality of trial or provisional articulating liners, which lack spring fingers for fixing the liner to the stem, but otherwise are substantially identical to the implanted articulating liner. Due to the lacking spring fingers these trial liners often wobble, piston or pivot out of position during trail reduction of a joint. Therefore, the surgeon does not obtain a true representation of the new joint and can get a false message during this critical operative step.